1. Field of the Invention
The present invention relates generally to wireless mobile terminals, and more particularly, to a method for charging a plurality of wireless power receivers using a single wireless power supplier.
2. Description of the Related Art
Mobile terminals, such as portable phones or Personal Digital Assistants (PDAs), are driven by a rechargeable battery. In order to charge the battery of the mobile terminal, a separate charger supplies electric energy to the battery. Typically, because respective contact terminals are provided on an exterior of both the charger and the battery, connectors between the contact terminals electrically connect the charger and the battery.
However, in the foregoing contact charging scheme, because the contact terminals are externally exposed, they may be easily contaminated, making it difficult to charge a battery. When the contact terminals are exposed to humidity, charging the battery cannot be normally performed.
Wireless or non-contact charging technology has been developed and applied to various electronic devices.
The wireless charging technology uses wireless power transmission and reception. For example, a wireless charging system is capable of automatically charging a battery when a portable phone is placed on a charging pad without being connected with a separate charging connector. In general, a wireless electric toothbrush and a wireless electric shaver are examples of wirelessly products that may be charged that are well known to ordinary persons. The wireless charging technology charges electronic devices in a wireless scheme to improve a water-resistance function. Because a wired charger is unnecessary, the portability of electronic devices is increased.
Examples of wireless charging technology include, for example, an electromagnetic induction scheme using a coil, and an RF/Micro Wave Radiation scheme for converting electric energy into a microwave and transferring the microwave.
Transmission of power over several meters has been accomplished using microwaves.
A power transmission scheme using electromagnetic induction refers to a scheme for transmitting power between a primary coil and a secondary coil. If a magnet is moved around a coil, an induction current is produced. An electric field is generated in a sending end and electric current is induced according to a change in the electric field to create energy. This is referred to as magnetic induction. The power transmission method using magnetic induction has excellent energy transmission efficiency.
An electromagnetic induction scheme has been used and applied to various devices. Most non-contact charging technologies used in conventional wireless charging are based on the electromagnetic induction scheme.
A system has been developed for transferring electric energy in a wireless scheme using a resonant type power transmission principle of a coupled mode theory as a resonant scheme, although it is spaced apart from a charger by several meters. This wireless charging system uses a physical concept of resonance meaning that, for example, a wine cup rings at the same vibration rate as a tuning fork oscillating beside the wine cup. An electromagnetic wave having electric energy is resonated instead of a sound. Because the resonated electric energy is directly transferred where there is a device having a resonant frequency, and a non-used part is spread to air but is again absorbed in an electronic field, it does not affect peripheral machines or persons, unlike an electromagnetic wave.
A wave radiation scheme is a power transmission scheme that converts power energy into a microwave beneficial to wireless transmission and energy transfer. Unlike a signal used in a wireless communication scheme, such as a radio or a wireless phone, the wave radiation scheme sends electric energy. A signal is loaded in a carrier wave and the carrier wave is sent in a general communication scheme.
In the foregoing wireless power transmission system, for efficient power transmission, communication may be performed between a wireless power supplier and a wireless power receiver. Conventionally, power from the wireless power supplier is supplied to the wireless power receiver, and the wireless power receiver unilaterally transmits a power communication signal capable of controlling an amount of supplied power to a wireless power device.
However, when there are a plurality of wireless power receivers, if respective wireless power receivers transmit a transmission signal in one direction, respective frequencies of the power communication signals collide preventing the ability to smoothly charge.